Kaszab Zoltán (szerk.): A Magyar Természettudományi Múzeum évkönyve 75. (Budapest 1983)

Szabó, J.: Lower and Middle Jurassic Gastropods from the Bakony Mountains (Hungary). Part V.: Supplement to Archaeogastropoda; Caenogastropoda

Genus ? VENTRICA RIA KOKEN, 1896 Ventricaria? vesicula sp. n. (Plate I: figs. 7-10) H o I o t y p u s : Plate I : fig. 7. — Lycus typicus: Bakonybél. Somhegy. — Stratum t y p i c u m : limestone infilling horizontal fissure. — Derivatio nominis : vesicula (Lat.) = small bubble (referring to the extremely thin shell and to the globular form). Diagnosis : extremely thin shell; ovate outline; convex whorls with angulation up to the penultimate whorl, which are just covered by the suture; cancellate ornament consisting of dense threads. Measurements: H HL HA D W A Plate I: fig. 7. — 24 15 12 Material — Five fragmentary specimens. Shape — The shell is dextral, thin-walled, oval in outline. The whorls are convex, the suture runs in a shallow groove. The periphery is angular in the juvenile specimens, with the suture running on this very angulation. This angulation disappears on the penultimate whorl, and the last whorl is slightly inflected. The somewhat thickened outer lip of the last peristome is trumpet-like except its basal part, what is projected slightly, thus the columellar lip bends forward, too. On the relatively wide anterior surface of this latter peristomal part an axially elongated depression is visible. The duplication of the shell shows that this surface is actually a callus, which probably closes also a previously open umbilicus. The margin of the callus coincides with an angulation of the convex base bordering the presumed umbilicus. The adapical end of the columellar lip and the parietal lip cannot be freed out on the single specimen with preserved peristome. The embryonal shell is similarly unknown. Ornament — The ornament is fine, net-like, with spiral threads thinner and denser than the intersecting ones. These latters are prosocline to the angulation or to the corresponding level on the last whorl, then are slightly opisthocyrt with maintained prosocline tendency. Distribution — Bakonybél, Somhegy : condensed Subfurcatum and Garantiana Zones. Remarks — Similar shape is common in the terrestrial gastropods, but no diagnostic traces of land in the Middle Jurassic of the Bakony Mts. are known. Similarly-shaped genera of uncertain systematic position are united in Codonocheilidae, and species of the genus Ventricaria seem as most closely allied forms. Some visible differences: V.? vesicula sp. n. has lower spire than other species of the genus; the transvese ornament is stronger than the spiral one; the presevred youngest whorls do not suggest an apex sharpening so much as in the Ventricaria species; so, until clarification of this last morphological character, the generic arrangement remains uncertain. From the two rather similar Mesozoic genera of the family, Bathyclides STRAND, 1928 has a phaneromphalous shell, and Pirper DE GREGORIO, 1886 shows smooth shell. Both genera have whorl surface without angulations which are Fig. 2. Shape of Ventricaria! vesicula sp. n., reconstructed after the specimens figured on Plate I: figs. 7-9, Xl.l